1. Field of the Invention
The present invention relates to an air jet for producing a filter plug for a cigarette; the filter plug of which has suitable filtration properties for removing tar and/or nicotine from a tobacco smoke stream with a lesser amount of tow-like fiber bundle filled in one filter plug. The filter plug formed by the air jet according to the present invention also has a high initial hardness as well as a high equilibrium hardness. Further the air jet according to the present invention has the ability to effectively form a filter plug from various fiber bundles having different total denier.
2. Description of Prior Arts
Indispensable characteristics for an air jet used in a filter plug machine when a filter plug is formed from a tow-like fiber bundle are as follows:
(1) The air jet must impart a sufficient propelling force to any tow-like fiber bundle having various total denier in a range of several thousand deniers through several tens of thousand deniers so that the fiber bundle can be smoothly and effectively delivered to a tongue of a filter plug machine and converted to a filter plug.
(2) The air jet must form a filter plug having a suitable filtration ability for removing tar and/or nicotine from a tobacco smoke stream with a lesser amount of tow-like fiber bundle filled in the filter plug.
(3) The air jet must form a filter plug having a high initial hardness as well as a high equilibrium hardness for enhancing ease of handling and preventing deformation thereof during smoking.
Conventionally, a tow-like fiber bundle containing an increased amount of plasticizer (generally triacetin) is used for obtaining a filter plug having a high equilibrium hardness so that the bonding points between fibers constituting the filter plug increase. In fact, the resultant filter plug has a high equilibrium hardness, but has the drawback that it softens because of the moisture contained in a smoke stream when smoked in combination with tobacco cylinder.
Another way to obtain a filter plug having a high initial hardness as well as a high equilibrium hardness is to increase the quantity of tow-like fiber bundle in one filter plug. The filter plug thus obtained, however, has drawbacks in that many punctures occur in the resultant filter plugs directly after formation thereof and the air suction resistance of the filter plug is so high that its aptitude as a cigarette filter is lowered.
In addition, it is necessary to form a filter plug with a tow-like fiber bundle of increased quantity such that the fiber bundle must be fed to a tongue of a filter plug machine with a higher propelling force. However, an air jet that can impart such a high propelling force to the fiber bundle has not yet been developed.
While, attempts to obtain an air jet satisfying the above indispensable characteristics (1) through (3) have been made. For example, Japanese Examined Utility Model Publication No. 60-796 discloses an air jet having a cross-section shown in FIG. 1. The air jet of this type is characterized by the provision of slits at a beak-like exit end so that a higher pressure air stream can be used relative to a conventional transport type air jet, whereby a tow-like fiber bundle can be fed to a tongue of a filter plug machine with a high propelling force. However, if a filter plug having a high initial hardness is formed while using this air jet, the amount of tow-like fiber bundle filled in one filter plug is increased and air suction resistance thereof becomes higher.
In Japanese Unexamined Utility Model Publication No. 2-29296, an air jet is disclosed for feeding a tow-like fiber bundle containing a plasticizer and having active carbon particles adhered on one side thereof to a filter plug machine. The air jet is adapted to minimize the drop-off of the active carbon particles from the fiber bundle by an air stream during movement of the fiber bundle to the filter plug machine. As shown in FIG. 2, this air jet comprises an inner tube 2 having a fiber path 3 therein and an outer tube 1 encircling the inner tube 2. An air circulation chamber 4 is provided between both tubes 1, 2. A plurality of air guiding walls 5a, 5b, 5c and 5d are formed lengthwise on an outer surface of the inner tube 2, while encircling the same. A plurality of air nozzles 6a, 6b, 6c and 6d are provided at the respective base portions of the air guiding walls, while slanting in the travelling direction of the fiber bundle and communicating from the interior of the air circulation chamber of the inner tube to the fiber path. Air inlet ports 8, 9 are provided on the outer tube 1 at the upstream end and the downstream end thereof, respectively. An air suction slit 11 is formed between an air deviation guide 10 provided in the downstream area of the fiber path of the inner tube and the downstream end air guiding wall 6b so that air ejected into the fiber path is circulated into the air circulation chamber and the active carbon particles dropping off from the tow-like fiber bundle during transportation by the air jet are again fed to the fiber bundle by high pressure air. This air jet in fact can feed the fiber bundle to a garniture portion of a filter plug machine while preventing the active carbon particles from dropping off from the fiber bundle, but has the drawback that a satisfying filter plug having a high initial hardness is not usually obtained.